Large motorcycles are often the pride of their owners. These machines are especially appreciated for their distinct appearance, distinct sound and high performance. Generally, the owners of large motorcycles are independent, original and creative individuals who like to appose a personal touch to the appearance or to the engine performance of their motorcycles. Therefore, original equipment manufacturers as well as generic component fabricators offer large assortments of custom parts and accessories for customizing these motorcycles to satisfy a great number of different preferences.
A common modification performed by motorcycle owners is the replacement of the original rear wheel tire by a wider one. This modification enhances the expression of power and performance of the machine.
The original rear wheel tire on a Harley-Davidson Softail.TM. motorcycle is a series 130 mm (5.1 inches). The width of the frame allows for the installation of a series 160 mm (6.3 inches) tire. This modification requires the displacement of the transmission, the inner primary housing and the rear sprocket, toward the drive side of the engine, and the replacement of the drive shaft extension with a longer one. A component kit for doing this modification, is available from Vulcan Engineering Company, from Manchester, N.H., U.S.A. A two-page product bulletin no. 3131 describing this kit is incorporated herein by reference.
A major obstacle to the placement of a wider rear wheel tire on those motorcycles is the maximum available space inside the swing arm of the rear wheel suspension, and the space taken up by the flat drive belt between the rear wheel and the left arcuated side plate of the swing arm.
It is known that the more audacious handymen have successfully installed rear wheel tires larger than those of a series 160 mm (6.3 inches) on these motorcycles. This was done by cutting and welding and drastically modifying the original frame of the motorcycle. These modifications are often done at the expense of adversely affecting the alignment of both wheels, changing the original center of gravity of the motorcycle, or loosing the original strength of the frame. For safety reasons, modifications to the main frame of the motorcycle are not recommendable.